(+)-Methamphetamine ((+)METH) abuse has become America's number one drug threat (NACO, 2005) and effective treatment strategies for abuse of (+)METH and related stimulants are greatly needed. Current pharmacotherapies for managing the acute cardiovascular system, central nervous system and toxic effects are mostly supportive (Sato, 1992; Albertson et al., 1999; Richards et al., 1999); and do nothing to remove the drug from its sites of action in the brain. Also lacking are medications that can reduce or treat the medically crippling effects of (+)METH addiction. Antibodies provide an attractive potential medication that can target the drug instead of the site of action (Kosten and Owens, 2005). These high affinity protein-based medications act as so-called pharmacokinetic antagonists, sequestering the drug in the bloodstream away from medically vulnerable tissues like the brain and heart.
Unlike nicotine and cocaine where the effects are caused by a single, specific compound, drugs like opiates (e.g., morphine), arylcyclohexylamines (e.g., phencyclidine) and amphetamines (e.g., (+)METH) are starting structures from which many pharmacologically similar compounds can be synthesized. These so-called “designer drugs” can be chemically modified to alter their effects. Thus, for an antibody to have the broadest medical applicability, it should have high affinity and specificity for other medically important members of this drug class (i.e., (+)METH, (+)AMP and (+)MDMA).
There are other medication design issues that further complicate the development of effective treatments for (+)METH-like stimulants. First, (+)METH is one of several stimulant drugs of abuse with similar or overlapping effects. In particular, (+)AMP is both a pharmacologically active metabolite of (+)METH and a frequently used drug of abuse that could be substituted for (+)METH. Second, (+/−)-3,4-methylenedioxymethamphetamine is the racemic mixture commonly referred to as MDMA or ecstasy. The plus isomer ((+)MDMA) has predominately dopaminergic, stimulant-like activity with overlapping effects with (+)METH, while (−)MDMA has predominately serotonergic effects (Cho and Segal, 1994). (+)METH, (+)AMP, and (+)MDMA can produce life threatening effects at high doses (Cho and Segal, 1994; Farre et al., 2004). Additionally, all of these drugs are plus stereoisomers, with the minus isomers having a significantly different pharmacological profile of effects. For example, (−)-methamphetamine is commonly used as a bronchodilator in over the counter medications. The minus isomers of these drugs could potentially be purposely taken by drug abusers to neutralize mAb medications with high affinity binding for both plus and minus stereoisomers. In a related way, there are many structurally similar compounds like ephedrine and pseudoephedrine that could be used to lessen the efficacy of antibodies if the antibody is not highly specific for (+)METH-like structures.
Hence, there is a need in the art for haptens designed to elicit an immune response that may generate specific antibodies that recognize at least one or more of (+)methamphetamine, (+)amphetamine, or (+)MDMA, and that do not substantially cross-react with (−)methamphetamine, (−)amphetamine, or (−)MDMA, or over the counter medications.